Cummins/Onan — Voltage Regulator Test
Testing & diagnosis
From a Cummins/Onan service manual — check it applies to your exact model before use.
Applies to: Cummins/Onan MDKAD, Cummins/Onan MDKAE, Cummins/Onan MDKAF
Before you start
- Electrical shock can cause severe personal injury or death. Do not touch electrical wiring or components during testing.
Procedure
- Stop genset.
- Unplug voltage regulator from wiring harness.
- Connect a 6-volt lantern battery to F1-F2 terminals (pins 1 and 8) using jumpers and spare plug.
- Start genset.
- Measure output at S2-Q1 (pins 4 and 3) and Q1-Q2 (pins 3 and 5).
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- S2-Q1 output should be 120 VAC ± 20 VAC
- Q1-Q2 output should be 140 VAC ± 10 VAC
Full service-parts list: Cummins/Onan MDKAD →, Cummins/Onan MDKAE →, Cummins/Onan MDKAF →
Source: Cummins/Onan service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.